Densely spaced fins for semiconductor fin field effect transistors

ABSTRACT

A method of forming a fin-based field-effect transistor device includes forming one or more first fins comprising silicon on a substrate, forming epitaxial layers on sides of the one or more first fins, and removing the one or more first fins to form a plurality of second fins.

BACKGROUND

The present invention relates to fin field-effect transistors (finFETs), and more specifically, to densely spaced fins for semiconductor finFETs.

Field-effect transistors (FETs) generate an electric field, by a gate structure, to control the conductivity of a channel between source and drain structures in a semiconductor substrate. The source and drain structures may be formed by doping the semiconductor substrate, a channel region may extend between the source and the drain on the semiconductor substrate and the gate may be formed on the semiconductor substrate between the source and drain regions.

The size of FETs has been reduced through the use of fin-based FETs (finFETs), in which the channels of the FET are fin-shaped. Fins of a finFET use a vertical channel structure to increase the surface area of the channel exposed to the gate. As a result, the gate has a greater influence on the channel, because the gate is formed to cover multiple sides of the channel.

The continued miniaturization of electronics has required finFETs to be made continually smaller. However, the size of the fins and the spaces, or pitch, between fins is limited by the lithographic or other etching techniques used to form the fins. One technique currently used to form fins of finFET semiconductor devices is sidewall image transfer (SIT). In SIT, a sidewall spacer is formed on a sacrificial structure, such as a mandrel, which is defined in the present specification as a narrow band of material. The sacrificial material is removed, and the sidewall spacers are then used to etch fins in a silicon-based substrate. In conventional SIT processes, the width of the mandrels and the spaces between the mandrels define the pitch of the fins of the semiconductor device.

SUMMARY

According to one embodiment of the present invention, a method for forming a fin-based field-effect transistor (finFET) device includes forming one or more first fins comprising silicon on a substrate, forming epitaxial layers on sides of the one or more first fins, and removing the one or more first fins to form a plurality of second fins.

According to another embodiment of the present invention, a semiconductor device includes a silicon substrate, a plurality of epitaxially-grown fins extending from the silicon substrate, and a gate structure covering a portion of one or more of the epitaxially-grown fins to separate the fin into source/drain portions.

Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates an intermediate finFET semiconductor device according to an embodiment of the invention, including a photoresist layer for etching;

FIG. 2 illustrates the intermediate finFET semiconductor device of FIG. 1 following an etching process to form mandrels;

FIG. 3 illustrates the intermediate finFET semiconductor device of FIG. 2 after removal of the a silicon nitride cap;

FIG. 4 illustrates the intermediate finFET semiconductor device of FIG. 3 after forming a spacer layer according to an embodiment of the invention;

FIG. 5 illustrates the intermediate finFET semiconductor device of FIG. 4 following a spacer etch according to an embodiment of the invention;

FIG. 6 illustrates the intermediate finFET semiconductor device of FIG. 5 after a spacer-pattern etching process according to an embodiment of the invention;

FIG. 7 illustrates the intermediate finFET semiconductor device of FIG. 6 after an oxide fill according to an embodiment of the invention;

FIG. 8 illustrates the intermediate finFET semiconductor device of FIG. 8 having a sacrificial layer formed according to an embodiment of the invention;

FIG. 9 illustrates the intermediate finFET semiconductor device after forming a device region including silicon fins based on the sacrificial layer pattern according to an embodiment of the invention;

FIG. 10 illustrates the intermediate finFET semiconductor device of FIG. 9 following removal of the sacrificial layer according to an embodiment of the invention;

FIG. 11 illustrates the intermediate finFET semiconductor device of FIG. 10 after epitaxially forming densely-spaced fins on sides of the silicon fins according to an embodiment of the invention;

FIG. 12 illustrates the intermediate finFET semiconductor device of FIG. 11 after an oxide fill according to an embodiment of the invention;

FIG. 13 illustrates the intermediate finFET semiconductor device of FIG. 12 following removal of a mask from the silicon fins according to an embodiment of the invention;

FIG. 14 illustrates the intermediate finFET semiconductor device of FIG. 13 following removal of silicon fins and oxide material to cause the densely-spaced fins to be free-standing according to an embodiment of the invention; and

FIG. 15 illustrates a finFET semiconductor device according to an embodiment of the invention.

DETAILED DESCRIPTION

Fin-based field-effect transistors (finFET) devices are typically formed using etching processes, such as by photolithography, to form fins, and gates are formed on the fins. However, the distances between the fins are limited according to the etching processes used.

FIG. 1 illustrates a cross-section of an intermediate fin field-effect transistor (finFET) device 100 a according to an embodiment of the invention. In the present specification and claims, an “intermediate” finFET device is defined as a finFET device in a stage of fabrication prior to a final stage. The finFET device 100 a includes a silicon (Si) substrate 101, a mandrel layer 102, such as a silicon germanium (SiGe) layer 102, formed on the Si substrate 101, and a first hard mask layer 103 formed on the SiGe layer 102. In one embodiment, the first hard mask layer 103 is made of silicon nitride (SiN). A second hard mask layer 104 is formed on the first hard mask layer 103. In one embodiment, the second hard mask layer 104 is silicon dioxide (SiO₂).

A mandrel layer 105 is formed on the second hard mask layer 104. The mandrel layer 105 may be a silicon-based layer. A third hard mask layer 106 is formed on the mandrel layer 105. The third hard mask layer 106 may be made of SiN. A sacrificial layer 107 is formed on the third hard mask layer 106. The sacrificial layer 107 may be an organic planarization layer (OPL). In one embodiment, and anti-reflective coating 108 is formed on the sacrificial layer 107. The anti-reflective coating 108 may be a silicon anti-reflective coating (SiARC). A patterned photoresist layer 109 is formed on the anti-reflective coating 108. The pattern of the photoresist layer 109 may correspond to narrow bands, or mandrels, such that an etching process using the photoresist layer 109 results in mandrels being formed.

Embodiments of the invention encompass various materials and thicknesses of layers of the intermediate finFET device 100 a. For example, in one embodiment, the third hard mask layer 106 has a thickness of around 180 Angstroms (Å), the mandrel layer 105 has a thickness of around 1000 Å, the second hard mask layer 104 has a thickness of around 300 A, and the first hard mask layer 103 has a thickness of around 400 Å.

In FIG. 2, an intermediate fin field-effect transistor (finFET) device 100 b is shown having after an etch process by which the pattern of the patterned photoresist layer is transferred through the anti-reflective coating 108 and the sacrificial layer 107 so as to form mandrels 110, each including a base portion 110 a formed of the mandrel layer 105 and a cap portion 110 b formed of the third hard mask layer 106. In one embodiment, the coating 108 and sacrificial layer 107 are removed through a reactive ion etching (RIE) process, such as in a N₂H₂ ambient atmosphere.

In FIG. 3, an intermediate fin field-effect transistor (finFET) device 100 c is shown on which the cap portions 110 b have been removed to leave the base portion 110 a of the mandrels intact and free-standing. In one embodiment, the cap portions 110 b are removed by a wet etch process, such as using hot phosphorus.

In FIG. 4, an intermediate fin field-effect transistor (finFET) device 100 d is shown having a spacer layer 111 formed on the base portion 110 a of the mandrels and the second hard mask layer 104. The spacer layer 111 is formed on the top and sides of the base portion 110 a of the mandrels. In one embodiment, the spacer layer 111 is formed of SiN. The spacer layer 111 may be formed by any process, including any deposition process to deposit the SiN on exposed surfaces of the base portion 110 a of the mandrels and the second hard mask layer 104. Since the pitch between the mandrels is small (between 40-60 nm), the SiN spacer (spacer layer 111) needs to be deposited with good gap fill and conformity by molecular layer deposition (MLD).

In FIG. 5, an intermediate fin field-effect transistor (finFET) device 100 e is shown having the spacer layer 111 and base portion 110 a of the mandrels etched to form spacers 112. In particular, the horizontal portions of the spacer layer 111 are first removed by anisotropic etching so as to expose the base portion 110 a of the mandrels. This is followed by removal of the base portion 110 a of the mandrels, resulting in free-standing spacers 112. The etching may be any type of etching, including chemical etching.

In FIG. 6, an intermediate fin field-effect transistor (finFET) device 100 f is shown on which an etching process has been performed to transfer the pattern of the spacers 112 of FIG. 5 into the layers below. In particular, the etching forms narrow bands, which may be referred to as fins 112, or secondary mandrels 112. The fins 112 include a base portion 112 a made of the SiGe layer 102, and a cap 112 b made of the first hard mask layer 103.

In FIG. 7, an intermediate fin field-effect transistor (finFET) device 100 g is shown having spaces around the fins 112 filled by an oxide layer 113. The filling may occur by any deposition process. In addition, a chemical-mechanical planarization (CMP) or polishing process may be performed to flatten out an upper surface of the oxide layer 113 and fins 112.

In FIG. 8, an intermediate fin field-effect transistor (finFET) device 100 h is shown having a sacrificial layer 114 formed on the oxide layer 113, an anti-reflective coating layer 115 formed on the sacrificial layer 114, and a photoresist layer 116 formed on the anti-reflective coating layer 115. The sacrificial layer 114 may be an organic planarization layer (OPL). In one embodiment, the anti-reflective coating 115 is a silicon anti-reflective coating (SiARC). The photoresist layer 116 may have an opening 117 to define a device region. While one opening is illustrated in FIG. 8, it is understood that embodiments encompass openings of any desired shape to define semiconductor fin-based devices of any desired shapes.

In FIG. 9, an intermediate fin field-effect transistor (finFET) device 100 i is shown having in which an etch process has been performed to etch the sacrificial layer 114 and oxide layer 113. In addition, the anti-reflective coating 115 and the photoresist layer 116 have been removed to expose the device region 118. The fins 112 or secondary mandrels 112 are exposed in the device region 118 and are buried in the oxide layer 113 in the non-device regions. In one embodiment, the depth of the etch in the oxide layer 113 is controlled using a timed etch, instead of using an end-pointed RIE process.

In FIG. 10, an intermediate fin field-effect transistor (finFET) device 100 j is shown having the sacrificial layer 114 removed, such as by mechanical or chemical planarization or polishing or etching.

In FIG. 11, an intermediate fin field-effect transistor (finFET) device 100 k is shown in which layers of silicon 119 are epitaxially grown onto sides of the exposed fins 112 in the device region 118. In one embodiment, the bases 112 a of the fins are made of SiGe and the epitaxial layers 119 are made of silicon. In one embodiment, the epitaxial layers 119 only grow on the SiGe portions of the fins 112 corresponding to the mandrel layer 102 of FIG. 1, and not on the hard mask portions of the fins 112 corresponding to the hard mask layer 103 of FIG. 1.

In FIG. 12, an intermediate fin field-effect transistor (finFET) device 1001 is shown having spaces around the fins 112 filled in with the oxide material 113. The filling may occur by any deposition process.

In FIG. 13, an intermediate fin field-effect transistor (finFET) device 100 m is shown having the caps 112 b removed from bases 112 a of the fins 112. The removal may be by any etching process, including chemical, laser, or any other appropriate etching process.

FIG. 14 illustrates an intermediate finFET device 100 n having the bases 112 a of the fins 112 removed and the oxide layer 113 a etched back to expose the epitaxially-grown layers 119 as free-standing fins. In one embodiment, the fins 119 extend into the oxide layer 113 a and are separate from each other in the oxide layer 113 a.

FIG. 15 illustrates a fin field-effect transistor (finFET) assembly 400 according to an embodiment of the present invention. The finFET assembly 400 includes the substrate 401, a first finFET device 410 a, a second finFET device 410 b, and a third finFET device 410 c. While only three finFET devices are illustrated for purposes of description, embodiments of the invention encompass any number of finFET devices. The first finFET device 410 a includes merged source/drain (SD) regions 417 a, including a filling layer 419 a, or dielectric layer 419 a, formed around a fin 418 a, and a contact layer 420 a formed on the dielectric layer 419 a. A gate structure 421 a is located between the SD regions 417 a, and the gate structure includes a contact 422 a.

Similar to the first finFET device 410 a, the second finFET device 410 b includes merged source/drain (SD) regions 417 b, including a filling layer 419 b, or dielectric layer 419 b, formed around a fin 418 b, and a contact layer 420 b formed on the dielectric layer 419 b. A gate structure 421 b is located between the SD regions 417 b, and the gate structure 421 b includes a contact 422 b.

The third finFET device 410 c includes merged source/drain (SD) regions 417 c, including a filling layer 419 c, or dielectric layer 419 c, formed around multiple fins 418 c and 418 d, and a contact layer 420 c formed on the dielectric layer 419 c. A gate structure 421 c is located between the SD regions 417 c, and the gate structure 421 c includes a contact 422 c.

In embodiments of the invention, densely-spaced fins for finFET devices are formed by epitaxially growing the fins on sides of narrow bands of silicon, also referred to as mandrels, or fins. The mandrels may be formed by an SIT process, which is limited to forming fins up to a first predetermined density. By epitaxially growing fins on the mandrels and removing the mandrels, the fins may have a second density that effectively doubles that of the SIT process, or halves the pitch between fins, allowing for the fabrication of compact finFET circuitry.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated

The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention.

While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described. 

What is claimed is:
 1. A method of forming a fin-based field effect transistor (finFET) device, comprising: forming one or more first fins comprising silicon on a substrate; forming epitaxial layers on sides of the one or more first fins; and removing the one or more first fins to form a plurality of second fins.
 2. The method of claim 1, wherein the first fins include a base of silicon germanium and a cap of silicon nitride, and the epitaxial layers are formed only on the silicon germanium portions of the first fins.
 3. The method of claim 1, further comprising: forming a gate structure on the plurality of second fins to define source and drain regions; and forming a contact on the plurality of second fins.
 4. The method of claim 3, further comprising: forming filler material on the plurality of second fins to expand a volume of the source and drain regions.
 5. The method of claim 4, wherein forming the filler material comprises epitaxially growing a silicon-based material on the plurality of second fins.
 6. The method of claim 1, wherein forming the epitaxial layers on the sides of the one or more first fins comprises: etching the one or more first fins from a silicon-based layer; filling spaces around the one or more fins with an oxide layer; etching a portion of the oxide layer to define a device region having the one or more fins exposed; and forming the epitaxial layers on the sides of the one or more fins in the device region.
 7. The method of claim 6, wherein etching the portion of the oxide layer includes forming a sacrificial layer on the oxide layer and forming a photoresist layer on the sacrificial layer, the photoresist layer having a region without photoresist defining the device region.
 8. The method of claim 1, wherein forming the one or more first fins comprises: forming a plurality of third fins by performing an etching process; forming a silicon-based spacer layer on the plurality of third fins; etching the silicon-based spacer layer and the plurality of third fins to form a plurality of fin-shaped spacers; and performing an etching process using the fin-shaped spacers as a mask to form the one or more first fins.
 9. The method of claim 8, wherein the silicon-based spacer layer is made of silicon nitride.
 10. The method of claim 8, wherein the fin-shaped spacers are formed on a layer of silicon dioxide, the layer of silicon dioxide is formed on a layer of silicon nitride, and the layer of silicon nitride is formed on a layer of silicon germanium, and the layer of silicon germanium and the layer of silicon nitride form the one or more first fins.
 11. The method of claim 10, further comprising: forming the layer of silicon germanium epitaxially on a silicon substrate.
 12. A semiconductor device, comprising: a silicon substrate; a plurality of epitaxially-grown fins extending from the silicon substrate; and a gate structure covering a portion of one or more of the epitaxially-grown fins to define source and drain portions on opposite sides of the gate structure.
 13. The semiconductor device of claim 12, wherein a distance between the epitaxially-grown fins is 40 nanometers (nm) or less.
 14. The semiconductor device of claim 12, wherein the epitaxially-grown fins extend into an oxide layer of the silicon substrate.
 15. The semiconductor device of claim 14, wherein each epitaxially-grown fin is separate from each other epitaxially-grown fin in the oxide layer.
 16. The semiconductor device of claim 12, wherein the epitaxially-grown fins are made of silicon.
 17. The semiconductor device of claim 12, further comprising filler material on the plurality of epitaxially-grown fins defining source and drain regions of the semiconductor device.
 18. The semiconductor device of claim 17, wherein the filler material comprises an epitaxially-grown silicon-based material formed around the plurality of epitaxially-grown fins. 